1. Field of the Invention
The present invention relates to an elastic wave device in which a protective film is provided on a piezoelectric substrate.
2. Description of the Related Art
In the related art, elastic wave devices have been widely used as resonators and band pass filters.
For example, Japanese Unexamined Patent Application Publication No. 2013-168864, which will be described below, discloses an elastic wave device that includes a piezoelectric substrate, interdigital transducer (IDT) electrodes, and a protective film formed so as to cover the IDT electrodes. In Japanese Unexamined Patent Application Publication No. 2013-168864, the protective film can be made of a dielectric material such as alumina or sapphire. In addition, the thickness of the above-mentioned protective film is 0.03λ to 0.5λ.
In recent years, along with simultaneous utilization of a plurality of bands, such as carrier aggregation, and high-speed communication, such as LTE, the electrical power applied to a filter has been increased. Accordingly, in an elastic wave device such as that described in Japanese Unexamined Patent Application Publication No. 2013-168864, there have been cases where the electrical characteristics vary and where the IDT electrode portion melts, as a result of an IDT electrode portion generating heat.
In this case, by forming a protective film, which is made of a dielectric material having a high thermal conductivity, on the IDT electrode portion, the heat is able to be dissipated. However, in order to sufficiently dissipate the heat, it is necessary to increase the film thickness of the protective film. In the case where the film thickness of the protective film on the IDT electrode is increased, the resonator characteristics may sometimes deteriorate.